Free piston machine



' air to be supplied to the outside.

Patented Oct. 26, 1948 FREE PISTON MACHINE Robert Huber, Paris, France, assignor to Raul Pateras Pescara, Lisboa, Portugal Application December 21, 1945, Serial No. 636,444 In France December 26, 1944 4 Claims. (Cl. 230-56) The present invention relates to free piston machines including at least one movable system and at least one return energy pneumatic accumulator, and it is more especially, although not exclusively concerned, among these machines, with free piston motor-compressors and auto-generators.

The chiei object of the present invention is to provide a machine of this kind which is better adapted to meet the requirements of practice than those used for the same purpose up to the present time.

Other objects of my invention will result from the following detailed description of some specific embodiments thereof, with reference to the accompanying drawings, given merely by way of example, and in which:

Fig. 1 diagrammatically shows, in longitudinal section, a free piston motor-compressor according to the invention.

Fig. 2 shows, on an enlarged scale, an arrangement according to the invention for use in such a machine.

I embodiment of the arrangement according to my invention.

In the example shown by the drawing, the

motor compressor includes, as shown by Fig. 1,

a motor cylinder i provided, in the middle part thereof, with a fuel injector 2, and two motor pistons 31, 32, adapted to open, at the ends of their outward strokes, respective inlet and outlet Ports (not visible on the drawing).

One of these motor pistons, for instance 31, is made rigid with a compressor .piston t slidable in a cylinder 8 so as to ensure, by its outer face, in chamber 51 of cylinder 5, the compression oi On the other hand, the inner face of piston t oompresses, in chamber 52 of cylinder 5, a certain amount of air which is transferred into a fluidtight casing t surrounding motor cylinder i, for use for the scavenging and feed of said motor cylinder. Chamber B1 is provided with an inlet valve I and a discharge valve 8 and chamber with an inlet valve 8 and a discharge valve ill.

The other motor piston 82 is made rigid with a piston il slidable in a cylinder l2 and which imprisons, in this cylinder, an air cushion which stores up, during the outward stroke of the motor pistons, a certain amount of energywhich is given back to the pistons during their inward strokes, thus ensuring said inward displacements thereof. 7 The reciprocating movable systems 31-4 on the parts, these two periods being separated from each other by two periods of closing extending on either side of the times at which movable system 32- is at the respective ends of its inward and outward strokes.

The space thus placed in communication with the inside of the pneumatic accumulator may be: either the surrounding atmosphere; or the inside of the casing in which is accumulated the air under pressure for the feed of motor cylinder i"; or again, when a scavenging pump is provided, the inside of this pump (which would therefore be analogous to that formed in chamber'bz); or, finally, any other space in which the pressure is predetermined.

In the two first mentioned cases, the pressure existing in the space that is periodically brought into communication with the inside of the accumulator is practically constant, at least for periods relatively long with respect to the time of a complete oscillation of the movable system. Therefore, the pressure in this space is practically constant during a full oscillation of the system and the pressure that determines the evolution of the pressures on the inside of the accumulator is the very pressure existing in this space. On the contrary, in the third of the cases above con-- sidered, the pressure inside the scavenging pump may be, during the period of communication corresponding to the outward stroke, essentially stant pressure during the whole of an oscillation,

can be adjusted at will during the working of the machine so as to be given different values. How- .ever, once the adjustment period is terminated,

these pressures will remain unchanged for a relatively long time.

The communication between the inside of the systems.

A particularly simple arrangement is shown by Figs. 2 and 4 and consists in providing, in the wall oi cylinder I 2, along the path of travel of piston ii, a communication conduit, for instance in the form or a groove or channel means ll, controlled by said piston. This groove II is so positioned and dimensioned as to ensure a suitable communication between, on the one hand, the inside the accumulator and, on the other hand. the space on the inner side of piston ll (casing I in the example '61 Fig. 1)

' According to my invention, this communication complies. with the conditions corresponding to the following considerations:

It is already known to ensure the starting of a free piston machine, and in particular or a i'ree piston motor-compressor or auto-generator, by means 01 air under pressure introduced into a uitable space of the machine, and in particular into one or several return energy pneumatic accumulators. The pressure oi this air is, at the beginning, different from that which is to exist during normal working conditions in the same space and it is gradually transformed, during the first oscillations of the machine (these oscillations constituting the starting period), into said normal value. This variation of pressure corresponds, for instance. to a gradual lowering thereoi when the initial pressure is higher than the normal pressure in question. In machines existing at the present time, this lowering of the pressure is obtained through means controlled as aiunction of the stroke of the movable system of the machine when the latter,.in the course of its inward stroke, moves beyond the normal end of said stroke. a

With the arrangement according to my invention, the gradual lowering oi the starting air pressure can b obtained withoutit being necessary for the movable system to move beyond the normal end of its inward strokes, this result being obtained by periodically placing the inside oi' the accumulator in communication with a space at a lower pressure, for instancecasing 8, in the manner above set iorth.

The evolution of the pressure to be obtained according to my invention is illustrated by the diagram of Fig. 3, in which the abscissas correspond to the displacements of the movable system and the ordinates to the pressures in the accumulator. The pressure in casing 6 is supposed to be equal to 9. At the beginning or the starting period, the pressure of the air mass is par, considerably higher than the maximum pres sure pa of the accumulator under normal working conditions. tween the accumulator air cushion and easing 8 The period 01' communication beonly to per, lower than psi. Thus, during several successive oscillations of the movable systems. the curve of the pressures in the air cushion is gradually lowered, so as finally to the stabilized along curve nil-pan, which is the pressure curve of the accumulator cushion for normal working conditions of the machine.

It is possible to obtain, by means or such an arrangement, a gradual reduction. distributed over several successive oscillations of the movable systern, of the pressure of the accumulator air cushion without any necessity of having recourse to a displacement toward the centre of the machine of the end 01' the inward stroke of said system beyond its normal position so as thus to open a supplementary exhaust port. However I may, in some cases, provide such a port I4 (Fig. 2), as safety means. This port ensures a further communication between accumulator l2 and easing 8 as soon as piston Ii moves in the inward direction beyond a position X (Fig. 2).

Of course, the section to be given to communication conduit I3 and the time for which the communication is open are to be determined in every particular case according to the data corresponding to this case. V

However, ii it is desired to obtain, in the same machine, through the same conduit or channel means i3 on the one hand the feed of air to the accumulator cushion during normal operation from a space at a predetermined pressure, for instance from casing 6 and, on the other hand, the gradual reduction of the pressure in the accumulator air cushion during the starting period by transfer of a portion of the starting air from this cushion to said space, it may prove necessary to give conduit l3 different cross-sections for the starting period and for normal operation, respectively.

This is due to the fact .that, in normal operation the section of the communication conduit must be relatively large for ensuring a sufllcient feed of air to the cushion, even in the case of an important air leakage past the packing rings of piston I I existing as a consequence of wear and tear.. Furthermore, if the working pressure of the machine is variable and i! the pressure existing in the accumulator cushion is to be correspondingly adjusted by varying the feed pressure thereof, the dimensions of the communication conduit must'be sufllcient for ensuring, in particular, a quick rise of the pressure in the cushion (drop of this pressure is always facilitated by leakage past the piston rings) These considerations may lead the constructor ,to make communication conduit l3 of relatively corresponds to the space between points d and e next outward stroke, as a consequence of the leakage that has taken place during this communication, the pressure in the air cushion ris s large cross section. a

On the contrary, during the starting period, the section of the communication conduit must as a rule be relatively small, so that a sufflcient number of oscillations take place between the beginning of the starting period and the return to normal pressure conditions in the cushion.

In order to comply with these different requirements. I provide means for varying the cross section when necessary. For instance, as shown by Fig. 4 said means include, inside conduit or channel means l3, a check valve l5 provided with an aperture I6 of relatively small section and applied against its seat by a spring i1. During the starting period, in which the air, escaping from the cushion toward casing 6, flows in the direction indicated by arrows the section oi'passage is the restricted section of apentu-re i6, valve l5 remaining applied on its seat. On the contrary,

during normal operation, which corresponds to the air flow taking place in the opposed direction, valvel5 opens and thus affords a much larger section of flow for said air.

When the cushion of the energy accumulator is housed in two spaces which communicate through a valve and one of which acts, before starting, as a reservoir containing a certain amount of starting air, it may be necessary, according to the invention, to provide means for keeping said valve fully opened during normal operation of the machine. Said means may, for instance, be constituted by a merespring tending to lift the valve from its seat and to apply it against an abutment corresponding to its opened position.

Fig. 1 shows an arrangement complying with this condition. According to this construction,

the cylinder l2 of the accumulator is in com-- munication with a chamber l8 through a conduit I9 adapted to be closed by a valve 20. This valve is made rigid with a piston- 2| provided with a pass-age 22 fitted with a check valve 23 subjected to the action of a spring 2d urging valve 23 toward its seat.

Piston 2| is mounted inside a cylinder 25 the outer end of which is provided with an air inlet conduit 26.

Furthermore, according to the invention, I provide a spring 21 coacting with valve 20 and tending to lift it from its seat and to apply it against an abutment 28. Spring 24 is sufliciently strong for producing a given pressure drop across passage 22.

This device works in the following manner:

Before starting, chamber i8 is filled with air under pressure fed through conduit 26. Due to the diiIerence of pressure produced between the respective sides of piston 2| by the provision of loaded valve 23 in passage 22, valve 20 closes against the action of spring 21, so thatchamber l8 can be filled.

For starting the machine, the pressure acting upon the outer face of piston 2! is reduced to a relatively low value for instance by placing conduit 26 in communication with the atmosphere, so that valve 20 opens and the starting air imprisoned in chamber l8 enters cylinder 12 and starts the machine.

As chamber l8 belongs to Iator, Valve as the machine is in operation. This permanent and full opening of said valve is ensured by spring 21, even when the minimum pressure pa (Fig. 3) of the energy accumulator drops below the pressure that acts, during operation of the machine, on the outer face of piston 2|.

Of course, the above described example has no limit-ative character. The means above described might as well be applied to the case of a free piston auto-generator. I might also, according to my invention, apply the above described means for gradually varying the pressure of the starting fluid during the starting period to the case of a machine in which the starting air would be introduced into a space other than the return energy accumulator, for instance int a compressor cylinder. In this case, means should be provided for closing, during normal working conditions of the machine, the, communication conduit through which a portion of the starting air can flow gradually from the starting space during the starting period.

In a general manner, while I have, in the above description, disclosed what I deem to be practhe energy accumu- 20 must remain fully opened as long tical and efilcient embodiments of the present inand form of the parts without departing from the principle of the present invention as' comprehended within the scope of the accompanying" claims. 7 What I claim is:

1. A free piston machine which comprisesy-"in combination, a motor cylinder, at least one motor piston movable in said cylinder, at least one return energy pneumatic accumulator including a cylinder and a piston operatively connected with said motor piston so as to form with said last mentioned cylinder a variable volume chamber for an air cushion, means for supplying said chamber, for the starting of the machine, with a mass of compressed gas greater than that present therein for normal working conditions, means forming a discharge space in communication with the end of said accumulator cylinder that is on the other side of said accumulator piston trom said chamber, channel means opening in the wall of said accumulator cylinder adapted to cooperate with said accumulator piston for conmeeting said chamber with said space for two periods of time of every reciprocation of said accumulator piston corresponding respectively to intermediate portions of the inward stroke and the outward stroke thereof, respectively, said space being, for at least'said periods, at a pressure lower than the pressure in said accumulator chamber for the same periods during the starting of the engine, whereby said channel means gradually reduce the mass of gas in said accumulator to its normal working value after some starting oscillations ofathe-motor piston, and means for giving the section of flow through said channel means two different values for opposed directions v of flow therethrough, respectively.

2. A free piston machine which comprises, in

combination, a motor cylinder, at least one motor piston movable in said cylinder, at least one return energy pneumatic accumulator including a cyilnder and a, piston operatively connected with said motor piston so'as to form with said last I mentioned cylinder a variable volume chamber for an air cushion, means for supplying said chamber, for the starting of the machine, with a mass of compressed gas greater than that present therein for normal working conditions, means forming a discharge space in communication with the end of said accumulator cylinder that is on the other side of said accumulator piston from said chamber, channel means opening in the wall of said accumulator cylinder adapted to cooperate with said accumulator piston for connecting said chamber with said space for two periods of time of every reciprocation of said accumulator piston corresponding respectively to intermediate portions of the inward stroke and the outward stroke thereof, respectively, said space being, for at least said periods, at a pressure lower than the pressure in said accumulator chamber for the. same periods during the starting small passage.

3. A free piston machine which comprises, in

cation with the end of said accumulator cylinder, and on the opposite side of said accumulator piston from said chamber, channel means formed in the wail of said accumulator cylinder and adapted to cooperate with said accumulator piston for connecting said chamber with said space. said space being for the connection period at a lower pressure than the pressure in said accumulator chamber for the same period during the starting of the engine, whereby said channel means gradually reduce the mass of gas in said accumulator to its normal working value after some starting oscillations oi! the and means controlling the ilow through said channel means whereby said flow in one direction is greater than the flow in the opposite direction. 1

4. A tree piston machine which compriseain combination, a motor cylinder, at least one motor piston movable insaid cylinder, at least one return energy pneumatic accumulator including a cylinder and a piston operatively connected with said motor piston so as to form with said last mentioned cylinder a chamber of variable volume acting as an air cushion, means for supplying said chamber, for the starting of the machine, with a mass of compressed gas greater motor piston,

than that present therein for normal working conditions, means forming. a discharge space in communication with the end of said accumulator cylinderwhich is on the other side of said accumulator to its normal working value after some satrting oscillations of the motor piston, and a check valve in said channel adapted to open toward said chamber and provided with a constantly open small passage.

- V ROBERT HUBER.

REFERENCES CITED The following references are of record in the file'of this patent:

UNITED STATES PATENTS Number Name Date 1,732,693 Pescara Oct. 22, 1929 2,086,162 Janicke July 6, 1937 2,222,260

FOREIGN PATENTS Country M Date Sweden Mar. 16, 1939 Great Britain May 15, 1930 OTHER REFERENCES Serial No. 418,666 (A. P. c. published June 15, 1943.

Number Janicke Nov. 19, 1940 

